How do I replicate what’s in this image (that equation followed by a number in parentheses) without using tabs? The equation needs to be centered, while the number stays aligned to the right margin.

Also, how can I set up page numbering so that pages a-b use Roman numerals, while pages c-d switch to standard Arabic numerals within the same document?

Also, how can I set up page numbering so that pages a-b use Roman numerals, while pages c-d switch to standard Arabic numerals within the same document?